Method for operating an electromechanical transducer system and electromechanical transducer system

ABSTRACT

For operating an electromechanical transducer system with at least one piezoelectric transducer element, if necessary at least one identification element and an electronic control unit, on the one hand, the wanted signals of a certain utility operating range defined by the frequency band and time window thereof, assigned to at least one piezoelectric transducer element, as well as, on the other hand, inquiry signals and response signals for the functional testing of the transducer system are transmitted via a line system with only one electrical signal line. 
     In order to thereby render possible a simple and reliable diagnosis method for the input circuit of cable break, with a corresponding increase in operational reliability, reduction of error search times and simplification of operation, at least one inquiry signal located outside the utility operating range of the transducer element is transmitted to the transducer system and from the resulting response signal at least one characteristic value is formed and at least one previously determined criterion is queried, wherein in the event of non-fulfillment of the criterion, an error message is generated.

The invention relates to a method for operating an electromechanicaltransducer system with at least one piezoelectric transducer element, atleast one identification element and an electronic control unit,wherein, on the one hand, the wanted signals of a certain utilityoperating range defined by the frequency band and time window thereof,assigned to at least one piezoelectric transducer element, as well as,on the other hand, inquiry signals and response signals for thefunctional testing of the transducer system are transmitted via a linesystem with only one electrical signal line, as well as anelectromechanical transducer system, comprising at least onepiezoelectric transducer element, in addition at least oneidentification element, and a line system with only one electricalsignal line for transmitting, on the one hand, the wanted signals of acertain utility operating range defined by the frequency band and timewindow thereof, assigned to at least one piezoelectric transducerelement, as well as, on the other hand, inquiry signals and responsesignals for the functional testing of the transducer system, as well asan electronic control unit.

In principle it is known for the testing or monitoring of the currentstate of a cable connection from and to sensors to carry out delay timemeasurements, which is complex, however, due to the necessity ofmeasurement and evaluation apparatus in this respect. This applies allthe more if cables of different lengths are used.

In the case of piezoelectric sensors—together with cable and plugconnector—a cable break detection is very difficult to establish due tothe required high insulation at the input of the charge amplifier. In EP423 273 B1 an arrangement is described in which changes to the resonantfrequency of piezoelectric elements were drawn on as indications of theoperational capability of the entire measuring chain, from the sensorvia the cable, etc. to the amplifier.

IN U.S. Pat. No. 5,821,425 a SAW element provided with a type ofpredetermined breaking point between the input and output transducer isdescribed as a break sensor. If a structure connected to a sensor ofthis type is mechanically damaged, an output signal can no longer bereceived, which then can be used as an indication of structural damage,but not of the operational capability of the measuring chain.

The object of the present invention is therefore a simple and reliablediagnosis method for the input circuit of cable break, with acorresponding increase in operational reliability, reduction of errorsearch times and simplification of operation.

To attain this object, the method described at the outset ischaracterized in that at least one inquiry signal located outside theutility operating range of the transducer element is transmitted to thetransducer system and from the resulting response signal at least onecharacteristic value is formed and at least one previously determinedcriterion is queried, wherein in the event of non-fulfillment of thecriterion, an error message is generated. The functional monitoring andthe measuring signal transmission can thus be separated well and bothoperations can take place uninfluenced by one another, if necessary atthe same time or overlapping.

According to a first embodiment variant of the method according to theinvention, it is provided that in a phase with ensured state anderror-free function of the transducer system at least one inquiry signalis transmitted to the transducer and from the resulting response signalat least one reference characteristic value is formed and saved, whereinthe adequate conformity in the operating phase of the respectivelycurrent characteristic value currently formed from the response signalwith this reference value is used as criterion.

If according to a further embodiment variant of the method at least oneinquiry signal is already transmitted before the first transmission of awanted signal, it can thus be ensured that the intended operation takesplace only when the transducer is correctly coupled and functional.

In a method variant in which an inquiry signal is transmitted at leastonce during the operating phase as intended of the transducer system,the proper operation can thus be monitored.

Advantageously, it is provided that the repetition frequency of theinquiry signals lies in the zero frequency band of the transducer.

According to an advantageous variant, it is provided that theidentification element operates purely passively and high-frequencyinquiry signals are used. Advantageously, the coupling of the inquiryunit thereby takes place in an inductive manner, but capacitive couplingor antenna coupling is also possible. The high frequency of the inquirysignal (typically in the range of more than 400 MHz) thereby permits anefficient coupling, in particular in the case of inductive coupling,without interaction with wanted signal and resonant frequencies of thetransducer element.

If the characteristic value formed from the response signal comprisesthe data of the identification signal contained in the response signal,at the same time as the functional monitoring a unique assignment of thetransducer system in the overall arrangement can be made.

A particularly simple embodiment variant of the method provides that oneof the electric variables current or voltage is applied with a constantvalue different from zero as an inquiry signal to the transducer system,that the respectively other of the two variables is detected as aresulting response signal, wherein the criterion for the error messageis a previously determined limit value for a characteristic value of thedetected variable.

According to a further embodiment, it can be provided that an integralvalue, proportional to the charge quantity, of a current detected as aresponse signal is used as a characteristic value.

The integral value reached during the duration of the inquiry signal canalso be used as a characteristic value.

Alternatively thereto, the integration duration until a predeterminedintegral value is reached can be used as a criterion characteristicvalue.

A further variant of the method according to the invention ischaracterized in that the increase rate of an integral value,proportional to the charge quantity, of a current detected as a responsesignal is used as characteristic value.

The increase in voltage can also be detected as the characteristic valueof the response signal.

Another variant according to the invention of the method provides that acurrent permanently applied to the transducer system anyway is used asan inquiry signal, wherein the deviation of a voltage resultingtherefrom from a constant voltage is used in the electronic control unitas a control variable for the current strength, and this controlvariable is used as a criterion.

Advantageously, the current applied permanently to the transducer systemfor the drift compensation of a charge amplifier can thereby be used asan inquiry signal and a control signal controlling the currentgeneration can be used as a criterion.

To attain the set object, the transducer system described at the outsetis characterized according to the invention in that the inquiry signalsare located outside the utility operating range of the transducerelement and that a module is implemented in the electronic control unitwhich forms at least one characteristic value from the response signaland generates an error message in the event of non-fulfillment of acriterion previously stipulated.

Advantageously, it is provided thereby that the repetition frequency ofthe inquiry signals lies in the zero frequency range of the transducer.

A further advantageous embodiment of the invention provides that theidentification element operates purely passively and the inquiry unitgenerates an inquiry signal with high frequency. A high-frequencyinquiry signal of this type, typically in the range of more than 400MHz, renders possible in particular an effective inductive coupling tothe transducer element without interaction with wanted signal andresonant frequencies of the transducer element. With other embodiments,units for capacitive coupling or antenna coupling would also bepossible.

Advantageously, a reference characteristic value obtained from the dataof the identification element is stored as a criterion. A uniquecharacteristic value can thus be connected to the unique identificationof the transducer system in the overall system.

According to an advantageous embodiment of the invention, the transducersystem is characterized in that a device is provided with which one ofthe electric variables current or voltage is applied with a constantvalue different from zero as an inquiry signal to the transducer system,and that a further device is provided, with which the respectively otherof the two values is detected as a resulting response signal, wherein apreviously determined limit value for a characteristic value of thedetected variable is stored as a criterion for the error message.

Thereby a device for determining an integral value, proportional to thecharge quantity, of a current detected as a response signal can beprovided for use as characteristic value.

Advantageously, the device for determining the integral value reachedduring the duration of the inquiry signal is designed as acharacteristic value.

Otherwise, it could also be provided that the device for determining theintegration duration until a predetermined integral value is reached isdesigned as characteristic value.

An embodiment would also be conceivable in which the device is designedfor determining the increase rate of an integral value, proportional tothe charge quantity, of a current detected as a response signal.

Another embodiment of the invention that is easy to realize ischaracterized in that a device for determining the voltage increase isprovided as a characteristic value.

According to another embodiment, a device can also be provided, withwhich a current is permanently applied to the transducer system and thedeviation of a voltage resulting therefrom from a constant voltage isused as control variable for the current strength and that this controlvariable is used as a criterion in the module.

An advantageous embodiment of the invention using tested components thatare usually present anyway is finally characterized in that a device forthe drift compensation of a charge amplifier is provided, the currentthereof permanently applied to the transducer system is used as aninquiry signal and that the control signal controlling the currentgeneration is used as a criterion in the module.

In the following description the invention is explained in greaterdetail based on exemplary embodiments with reference to the attacheddrawings.

FIG. 1 thereby shows very diagrammatically the simplest arrangementaccording to the invention,

FIG. 2 shows a circuit diagram of an electromagnetic transducer elementaccording to the invention,

FIG. 3 is a circuit diagram of a circuit for carrying out the methodaccording to the invention on the basis of the current-voltagecorrelation,

FIG. 4 is a diagram of the voltage curves occurring during an inquirywith the device of FIG. 3, and

FIG. 5 is a circuit diagram of a circuit that is expanded compared toFIG. 3 for carrying out the method according to the invention on thebasis of the current-voltage correlation.

The electromechanical transducer system sketched in FIG. 1 is composedof at least one piezoelectric transducer system 1, which preferably canbe provided with in addition at least one identification element 2.

This arrangement of transducer element 1 and identification element 2 isconnected to an inquiry unit 4 for the identification element 2 and anoperational unit 5 for operating the transducer element 1 via a linesystem with only one electrical signal line 3. The wanted signalsassigned to the piezoelectric transducer element 1 as well as theinquiry and response signals for functional testing of the transducersystem are transmitted via the line 3. Furthermore, an additionalelectronic control unit, which is not shown here, can be provided.

Each piezoelectric transducer system 1 has a certain utility operatingrange defined by a frequency band and time window. In order by thefunctional testing of the transducer system 1 now not to influence theintended operation thereof, the inquiry signals of the inquiry unit 4are located outside the utility operating range of the transducerelement 1. The inquiry signal or the response signal can thereby have amuch higher frequency, e.g., several decimal powers higher, than aregular measuring signal, whereby it is very easy to distinguish betweeninquiry signal or response signal and measuring signal. Typically, theinquiry signals for transducer elements 1 in the form of piezoelectricsensors are in the range of more than 400 MHz.

The response signal to the inquiry signals is evaluated in a module thatcan be implemented in the electronic control unit or also already in theinquiry unit 4 itself, wherein this evaluation comprises the formationof at least one characteristic value from the inquiry signal. If thischaracteristic value does not fulfill a previously determined criterionstored in the module, an error message is generated.

A piezoelectric transducer system 1 can be, for example, a piezoelectricpressure sensor in an arrangement for measurement data acquisition,which is connected via measurement sensor lines to a suitable measuringamplifier. The measuring amplifier can thereby be a separate device thatis connected via measuring signal lines 3 to a measurement dataevaluation unit 5, e.g., an index device or a test stand control. Themeasuring signal line 3 of the sensor 1 is simultaneously also aninquiry line for this sensor.

The inquiry unit 4 can advantageously be connected to the measuring dataevaluation unit 5 or integrated therein. The inquiry signal going viathe common measuring signal/inquiry line 3 is recorded and processed bythe measuring amplifier of the piezoelectric pressure sensor of thetransducer system 1 in that, for example, in succession a correspondingresponse signal is transmitted, e.g., as a pulse, pulse train or in adigital data transmission or as a signal of a certain frequency, etc.The response signal is thereby advantageously different from themeasuring signals in order to render possible an easy recognition. If noresponse signal arrives at the inquiry unit 4 of the measurement dataevaluation unit, it can be assumed that the cabling between the input ofthe measurement data evaluation unit and the associated measuringamplifier of the pressure sensor is faulty or not available, e.g., dueto a faulty cable or a cable not plugged or incorrectly plugged. Apossible cabling error can thus be limited to a small unit. Theconnection quality can also be tested by means of the evaluation of thesignal quality of the response signal, which also permits a diagnosis ofthe cabling.

As can be seen from FIG. 2 with a circuit diagram of the arrangement oftransducer element 1 and identification element 2, as identificationelement 2, for example, can be embodied as a SAW tag, and thus operatepurely passively. The inquiry signal generated by the inquiry unit 4 canthus be ideally inductively coupled at high frequency—compared to thewanted signals of the transducer element 1. Typically, the frequenciesof the inquiry signals for piezoelectric sensor systems are in the rangeof more than 400 MHz. On the other hand, however, a capacitive couplingcan also be provided, or also an antenna coupling. The capacity or theohmic resistance of the arrangement of transducer 1 and identificationelement 2 are represented in the circuit diagram by the capacity 6 andthe resistance 7 respectively.

This identification of the transducer system 1, which can also beintegrated in measurement amplifiers of sensors, for example, can beused for testing the configuration of a measurement arrangement or forthe automatic detection of this configuration. For example, if noresponse signal arrives at an input of the measurement data evaluationunit provided according to the stored configuration, or if this signalarrives at an incorrect input, a cabling error or a faulty cable can bepresent. Through individual inquiry of the transducer system 1 andchecking at which channel of a multichannel measurement data evaluationunit a specific response comes back, the configuration can be detectedand e.g. transferred to management software. The operating staff canalso be helped with the cabling in that e.g. during the cabling it iscontinuously tested whether the plugged cables also correspond to theprovided configuration.

In FIG. 3 a method is explained by means of a circuit diagram in which acurrent Iinp is applied with a constant value different from zero as aninquiry signal to the transducer system 1, 2. As a resulting responsesignal, the resulting voltage Uout is then detected, wherein thecriterion for the error message is a previously determined limit valuefor a characteristic value of the detected variable voltage. In theexample shown, the voltage increase is detected as the relevantcharacteristic value of the response signal, the course of which voltageincrease is shown in FIG. 4.

In normal measurement operation, the switch 8 in FIG. 3 is in the“operate” position. For a query, the switch is placed in the “test”position and thus a test voltage Utest is applied via a voltage source 9to the non-inverting input of the operation amplifier 11 switchedparallel to the condenser 10. The voltage curves shown in FIG. 4 resultthereby, wherein any line break can then be recognized from the courseof the output voltage Uout.

A further exemplary embodiment for concluding in the application of atest voltage a possible line break from the resulting output signal isshown in FIG. 5. An inquiry current Iinp is permanently applied to thetransducer system 1, 2 including cable 3, and the resulting voltage atthe input of the charge amplifier 12 is compared to the low offsetvoltage Uoffset, virtually always present, which is different from zero.In contrast to FIG. 3, here a test voltage is not fed to thenon-inverting input of the operation amplifier 12, but generated bymeans of a digital-analog converter 13, controlled via themicroprocessor 14 and fed as test current Id via the resistance 15 tothe inverting input of the operation amplifier 12. Any small deviationis here amplified as it were endlessly, detected at certain times by ananalog-digital converter with sample&hold element 15 and themicroprocessor 14 and used as control variable for the generation of theinquiry current.

The microprocessor 14 is moreover used to evaluate the output voltageUout caused by the test voltage and to detect a possible cable break. Tothis end a digital line is provided from the analog-digital converterwith sample&hold element 15 to the microcomputer 14 in order to querythis control variable. If this control variable exceeds a valuepredetermined as a criterion, then either the bias current or the straycurrent (Uoffset/Risolation) is too large.

1. A method for operating an electromechanical transducer system with atleast one piezoelectric transducer element, at least one identificationelement and an electronic control unit, wherein, on the one hand, thewanted signals of a certain utility operating range defined by thefrequency band and time window thereof, assigned to at least onepiezoelectric transducer element, as well as, on the other hand, inquirysignals and response signals for the functional testing of thetransducer system are transmitted via a line system with only oneelectrical signal line, wherein at least one inquiry signal locatedoutside the utility operating range of the transducer element istransmitted to the transducer system and from the resulting responsesignal at least one characteristic value is formed and at least onepreviously determined criterion is queried, wherein in the event ofnon-fulfillment of the criterion, an error message is generated.
 2. Themethod according to claim 1, wherein in a phase with ensured state anderror-free function of the transducer system at least one inquiry signalis transmitted to the transducer and from the resulting response signalat least one reference characteristic value is formed and saved, whereinthe adequate conformity in the operating phase of the respectivelycurrent characteristic value currently formed from the response signalwith this reference value is used as criterion.
 3. The method accordingto claim 2, wherein at least one inquiry signal is already transmittedbefore the first transmission of a wanted signal.
 4. The methodaccording to claim 3, wherein an inquiry signal is transmitted at leastonce during the operating phase as intended of the transducer system. 5.The method according to claim 4, wherein the repetition frequency of theinquiry signals lies in the zero frequency band of the transducer. 6.The method according to claim 5, wherein the identification elementoperates purely passively and high-frequency inquiry signals are used.7. The method according to claim 6, wherein the characteristic valueformed from the response signal comprises the data of the identificationsignal contained in the response signal.
 8. The method according toclaim 5, wherein one of the electric variables current or voltage isapplied with a constant value different from zero as an inquiry signalto the transducer system, that the respectively other of the twovariables is detected as a resulting response signal, wherein thecriterion for the error message is a previously determined limit valuefor a characteristic value of the detected variable.
 9. The methodaccording to claim 8, wherein an integral value, proportional to thecharge quantity, of a current detected as a response signal is used as acharacteristic value.
 10. The method according to claim 9, wherein theintegral value reached during the duration of the inquiry signal is usedas a characteristic value.
 11. The method according to claim 9, whereinthe integration duration until a predetermined integral value is reachedis used as a criterion characteristic value.
 12. The method according toclaim 8, wherein the increase rate of an integral value, proportional tothe charge quantity, of a current detected as a response signal is usedas characteristic value.
 13. The method according to claim 8, whereinthe increase in voltage is detected as the characteristic value of theresponse signal.
 14. The method according to claim 6, wherein a currentpermanently applied to the transducer system anyway is used as aninquiry signal, wherein the deviation of a voltage resulting therefromfrom a constant voltage is used in the electronic control unit as acontrol variable for the current strength, and this control variable isused as a criterion.
 15. The method according to claim 14, wherein thecurrent applied permanently to the transducer system for the driftcompensation of a charge amplifier is used as an inquiry signal and acontrol signal controlling the current generation is used as acriterion.
 16. An electromechanical transducer system, comprising atleast one piezoelectric transducer element (1), in addition at least oneidentification element (2), and a line system with only one electricalsignal line (3) for transmitting, on the one hand, the wanted signals ofa certain utility operating range defined by the frequency band and timewindow thereof, assigned to at least one piezoelectric transducerelement (1), as well as, on the other hand, inquiry signals and responsesignals for the functional testing of the transducer system (1, 2, 3),as well as an electronic control unit (4, 5), wherein the inquirysignals are located outside the utility operating range of thetransducer element (1) and that a module (4) is implemented in theelectronic control unit (4, 5) which forms at least one characteristicvalue from the response signal and generates an error message in theevent of non-fulfillment of a criterion previously stipulated.
 17. Thetransducer system according to claim 16, wherein the repetitionfrequency of the inquiry signals lies in the zero frequency band of thetransducer (1).
 18. The transducer system according to claim 16, whereinthe identification element (2) operates purely passively and the inquiryunit (4) generates an inquiry signal with high frequency.
 19. Thetransducer system according to claim 18, wherein a referencecharacteristic value obtained from the data of the identificationelement (2) is stored as a criterion.
 20. The transducer systemaccording to claim 19, wherein a device is provided with which one ofthe electric variables current or voltage is applied with a constantvalue different from zero as an inquiry signal to the transducer system(1, 2, 3), and that a further device is provided, with which therespectively other of the two values is detected as a resulting responsesignal, wherein a previously determined limit value for a characteristicvalue of the detected variable is stored as a criterion for the errormessage.
 21. The transducer system according to claim 20, wherein adevice for determining an integral value, proportional to the chargequantity, of a current detected as a response signal is provided for useas characteristic value.
 22. The transducer system according to claim21, wherein the device for determining the integral value reached duringthe duration of the inquiry signal is designed as a characteristicvalue.
 23. The transducer system according to claim 21, wherein thedevice for determining the integration duration until a predeterminedintegral value is reached is designed as characteristic value.
 24. Thetransducer system according to claim 21, wherein the device is designedfor determining the increase rate of an integral value, proportional tothe charge quantity, of a current detected as a response signal.
 25. Thetransducer system according to claim 20, wherein a device fordetermining the voltage increase is provided as a characteristic value.26. The transducer system according to claim 20, wherein a device (8, 9)is provided, with which a current is permanently applied to thetransducer system (1, 2, 3) and the deviation of a voltage resultingtherefrom from a constant voltage is used as control variable for thecurrent strength and that this control variable is used as a criterionin the module.
 27. The transducer system according to claim 21, whereina device (13, 14, 15) for the drift compensation of a charge amplifier(12) is provided, the current thereof permanently applied to thetransducer system (1, 2, 3) is used as an inquiry signal and that thecontrol signal controlling the current generation is used as a criterionin the module.